Why is throat cancer holding Kenyans by the neck?

By Gatonye Gathura

Medical experts are baffled why Kenya is leading the world in the incidence of throat cancer as well as its highly selective behaviour.

The cancer is also seen to be affecting younger people only in some parts of Kenya while its distribution almost equally between the sexes contradicts known trends elsewhere.

It is also seen as concentrating in specific geographical areas, ethnic communities and even families.

Kenya belongs to the African Esophageal Cancer Corridor (ESCC) which has the highest incidence of throat cancer in the world.

The corridor includes Malawi, Kenya, Uganda, Tanzania and parts of South Africa while other areas with high cancer incidence are China and Iran.

A why report published in June by local and international cancer experts comparing the incidence of throat cancer globally says the disease is now highest in Kenya.

The researchers from North Carolina Central University, US; University of Nairobi, Kenyatta National Hospital and Dalian University, China, had compared the incidence of throat cancer in Kenya with the other hotspots of China, Iran and South Africa.

In the report published in June in the American Journal of Digestive Disease had also included France, US and UK for comparison with Kenya recording the highest incidence of the disease globally.

The information is cited from the World Health Organization’s affiliated GLOBOCAN, the global custodian of world cancer data.

The data shows Kenya to have the highest rates of new cases of throat cancers and deaths compared to the other countries in both women and men.

Official statistics show EC or esophageal cancer to have high prevalence in Central Kenya, around the Lake Victoria region but with possible hotspots in Eldoret and Bomet in the Rift Valley.

Data at both the Moi Teaching and Referral Hospital in Eldoret and the Tenwek Mission Hospital in Bomet shows EC as the most prevalent cancer attended to at the two hospitals.

Doctors in these hospitals report what they say is a unique development of the EC not noted anywhere else.

EC patients around Bomet and Eldoret areas are getting the disease when they are much younger than those in other parts of the country or the world.

Cancers in this Rift Valley region of Eldoret and Tenwek are the only people getting throat cancer at age 10 or earlier with the prevalence reaching up to 10 per cent before ages 30.

The new study shows Tenwek to have the youngest throat cancer victims followed by Eldoret with cases in the two areas peaking by age 50.

This is different from other places on earth, for example any significant throat cancers in Nairobi are picked after age 30 and peaking at age 65. In the UK and US, significant numbers of throat cancer cases are being noticed at ages 50 and peaking at ages 70.

“Kenya currently has the highest reported percentage of young patients, below 30 years globally, and thus it is important to establish the reasons underlying so many young cases,” says the study lead by Joab Otieno Odera.

This and many other studies link alcohol drinking, smoking, dietary change and food preparation, and consumption of hot food or drink as the main risk factors for EC in Kenya.

However these behaviours are not unique to Tenwek and Eldoret areas in the country with experts saying they fail to answer some crucial questions.

This is also the opinion of an ongoing intense study at the 300 bed Tenwek Mission Hospital in Bomet supported by the US National Cancer Institute.

A description of the THINKER study, as it is called, says tobacco, alcohol diet and other lifestyle trends while important do not explain the high rates of EC in the region and its development in younger persons.

“Therefore, it is important to consider a wide range of causative factors to explain the high rates of cancer in these populations,” says the brief.

Towards this, the study is engaging 50 EC patients at Tenwek hospital whose tissue samples will be airlifted to the US for specialized studies including possible gene mutations.

EC is the most common cancer seen at Tenwek Hospital with 10 per cent of cases less than 30 years of age.

Another puzzle of EC in Kenya is its distribution among the sexes. While EC in almost all other parts of the world is almost three times higher in men compared to women in Kenya the burden is shared almost equally between the genders.

This puts into question risk such as alcohol and smoking where males are many times ahead of women yet sharing the risk of EC almost equally.

A study published in November the Nairobi Cancer Registry of Kenya Medical Research Institute (Kemri) showed various cancers were most likely to be found in specific ethnic groups.

For example in a 15 –year-period the registry had recorded high rates of deaths caused by throat cancer among the Kalenjin living in Nairobi.

Explaining the link between various cancers to particular ethnic groups the head of the registry Ann Korir suggested such groups may have continued with their cultural habits even after moving to Nairobi.

However scientists are reading a genetic play in the EC trends in the Rift Valley. For example, at Tenwek hospital Odera cites studies which found that 45 out of 60 patients had a family history of cancer and 21 out of 60 had a family history of EC.

Additionally, 25 patients had a first-degree relative suffering from cancer, and 16 patients had multiple relatives suffering from cancer.

Most of these patients, the study shows came from the nearby Kipsigis community, and therefore share a conserved gene pool.

“EC cases in children as young as 12 years and their family history suggest possible heritable germline mutations in EC,” concludes the study.

The researchers are recommending more work be done to understand the genetic link to the development of esophageal cancer is these geographic areas.